This application relates to an improved corrosion-inhibited alcohol antifreeze composition for use in the cooling systems of internal combustion engines. The invention also relates to a method for improving the anti-gel characteristics of antifreeze compositions which contain silicate corrosion inhibitors.
Antifreeze compositions containing alcohols, especially ethylene glycol, are commonly mixed with the cooling water in the cooling systems of internal combustion engines in order to depress the freezing point of the water and to increase the boiling point of the water. The alcohols gradually decompose in the cooling systems to produce acidic products which lower the pH of the antifreeze. It has been found that the metallic surfaces of the internal combustion engines become seriously corroded as the pH of the coolant decreases.
It has been known for many years that corrosion inhibitors must be added to the antifreeze compositions in order to retard the corrosion of the metal surfaces of the engines. Many such corrosion inhibitors are known. Alkali metal silicates are commonly used to reduce corrosion of aluminum heat rejecting surfaces. Antifreeze compositions containing such silicates generally have poor shelf life because of the tendency of the silicates to gel and/or form precipitates during storage.
It is an object of this invention to provide an improved silicate-containing antifreeze composition which has a longer shelf life because of improved anti-gel characteristics.
Certain silane compounds have been used in antifreeze compositions to improve the anti-gel characteristics of those compositions. U.S. Pat. Nos. 3,198,820 and 3,312,622 disclose the use of organic acid silane compounds for this purpose. U.S. Pat. No. 3,248,329 discloses the use of aminosilane compounds for this purpose. U.S. Pat. Nos. 3,337,496 and 3,341,469 disclose the use of hydroxy alkyl silanes for this purpose. U.S. Pat. No. 4,333,843 discloses glycol compositions containing a hydrolyzate of an organo phosphorus-silicon compound. Finally, United Kingdom patent application No. 2018266 discloses the use of phosphonate silanes for this purpose.
Prior to the present invention, it was felt that sulfur containing compounds should not be used in antifreeze compositions because of the highly corrosive nature of such compositions. Mercapto-containing compositions, of course, were included in this general prohibition. Unexpectedly, I have found that mercaptosilanes can be used in antifreeze compositions to improve the anti-gel characteristics thereof without increasing the corrosive nature of such antifreeze compositions.